ABSTRACT Minority gay, bisexual, or other men who have sex with men (MSM) contend with stigma and discrimination based on sexual orientation and race, resulting social isolation, and poverty risk that disproportionately impacts all minority groups. These factors contribute to mental/drug disorders, sex risk, and disproportionate STI/HIV, with half of black gay men and one-quarter of Hispanic gay men HIV-infected. Another prevalent social determinant of STI/HIV that disproportionately affects minority MSM, yet that remains largely unexamined in this group, is criminal justice involvement (CJI). CJI for many minority MSM begins early in the life course with police stops and searches; our preliminary studies in New York City indicate one-third of minority MSM approximately 20 years of age have been stopped and searched (or ?frisked?) in the past 12 months. CJI evolves to arrest and detainment and for many, incarceration, with approximately over half of some minority MSM groups experiencing jail or prison incarceration. Each step of the criminal justice process?being stopped by police, arrested, detained while awaiting trial often in over-crowded conditions, interacting with court-appointed lawyers?can be disempowering, demeaning, and for some may present physical threat. In other populations, CJI has been documented as a determinant of disrupted social and support networks, depression, substance use, and sex risk, in turn, culminating in STI/HIV infection. Our understanding of mediating pathways has informed development of programs for heterosexual minorities affected by CJI. This proposal is motivated by the prospect of developing policies and prevention programs for minority MSM. The effects of CJI on STI/HIV may differ for minority MSM; CJI may work synergistically with low social support, stigma/discrimination, and poverty to have particularly strong effects in this group. In addition, pathways linking CJI and STI/HIV risk also may differ for minority MSM. For example, while disruption of network ties may place minority MSM at risk, as we have observed in heterosexual minorities, other pathways may be equally critical because of high baseline risk of stigma and poverty. To address current critical gaps in our understanding of the effects of CJI on health, we have compiled a compendium of data sources to examine the effect of CJI on STI/HIV risk in minority MSM. Using the HIV Prevention Trials Network 061 (HPTN 061) cohort of black MSM and the Project 18 (P18) Cohorts 1 and 2 of minority MSM, we will evaluate longitudinal associations between multiple levels of CJI (stop-and- frisk, arrest, incarceration) and STI/HIV risk outcomes (e.g., sexual risk behaviors, STI, HIV, and viral load). We will describe the potential mediating roles of CJI-related disruption of social support networks, stigma, poverty, and resulting depression and substance use. In light of recent calls for changes to criminal justice policy, we aim to use computer simulation to model the impact of implementing polices to reduce CJI (e.g., decarceration) and improve correctional settings (e.g., by improving ties to community support networks through reduced costs of prison calls) on HIV transmission in minority MSM and the larger population. Findings will inform evidence-based discussions about how to modify policy and programs to best improve well-being and reduce HIV risk in a highly vulnerable population.